Exposure caused by weathering is unavoidable for materials in outdoor use. Such exposure results in particular from the UV component of solar radiation, via a great variety of different corrosion mechanisms, by cleaning operations, by wind-borne media (sand, dust), or by other, corresponding exposures in the specific application scenario. Unprotected or inadequately surface-coated materials lose their integrity and/or durability as a result. Materials based on metal substrates are subject, moreover, to a considerable potential for corrosion, thereby giving particular importance to the corrosion control aspect of the inventive coating.
WO 2014002964 describes powder coating formulations based on fluoropolymer resin and polyester polymers, this being an incompatible system with controlled separation of the two species.
Furthermore, the polyester component contains aromatic structural units which in principle, owing to their instability under the effect of solar radiation, are counterproductive for exposed outdoor use, from an aesthetic standpoint.
JP03-098276 A describes a formulation for powder coating, consisting of, among other components, a fluoropolymer and a crosslinkable polyester component.
This formulation technology, however, is not specifically designed for demanding outdoor use.
JP10-324843 A describes a coating resin formulation featuring a combination of weathering resistance and oil resistance, and also with the focus of an extremely low solvent fraction, based on a hydroxy-functional fluoropolymer having a defined (high) OH number; the design of this formulation is guided by the intended establishment of a very high oil resistance.
In this case, aromatics-based polyester formulations are permitted, such formulations being known to exhibit deficiencies in sustained weathering stability.
DE 10 2004 008 772 A1 describes an abrasion-resistant, alkali-resistant coating and also resultant moldings having a low-energy surface, with specific fluoropolymers being among the constituents.
The focus in this case, however, or the design of the formulation, is not on the provision of the surface profile of a combination of sustained corrosion control with outstanding—aesthetically sustained—surface coating.
AU 2002332335 B2 or WO 03/029368 A1 describes a powder coating formulation prepared from a fluoropolymer resin-based mixture with individual components with different glass transition temperatures, the aim being to ensure a combination of properties of sufficiently high blocking resistance on the one hand and also ease of processing at low temperatures on the other hand.
In this case it is likewise possible—optionally—for polyester resins to be employed. In this case, however, the formulation is not designed with the focus on a combination of sustained corrosion control with outstanding—aesthetically sustained—surface coating.
U.S. Pat. No. 6,365,276 B1 describes a coated metal article (produced by continuous coil coating), involving the use of an expensive fluoroethylene-vinyl ether-based coating formulation. In this case there is no further (co)binder employed, providing the possibility of little cost efficiency.
In diverse webinars (with a date of 13 Aug. 2014, for example), Asahi Glass Co. Chemicals, Lumiflon USA Division, has described the use of low molecular mass polyester diols (K-Flex 188, King Industries USA) as additive resins, admixed at comparatively low concentrations. Polyester diols of this kind, however, are unsuitable as co-binders and for the preparation of binder mixtures. The adverse effect on flexibility would be too great in this case.
The most widely known prior art in relation to corrosion-resistant and weather-resistant surface coating and surface decoration in the context of coil coating is practiced with what are called PVDF coating materials, but these materials have distinct design disadvantages since only the medium gloss range (25-35 gloss units, measured in the Gardner test at 60°) can be realized. Furthermore, coatings of this kind have a comparatively low surface hardness.